Somatostatin Induces Ectopic Activity Fronts of the Migrating Motor Complexes via a Local Intestinal Mechanism

Abstract

Somatostatin induces ectopic activity fronts of the migrating motor complex in man (1) and dog (2,3). It is not clear whether this is due to a central or to a peripheral effect of the hormone, because intraventricular administration of Somatostatin in the brain of rats (4) also increases the frequency of activity fronts in the small bowel. To study the peripheral effect of Somatostatin a tiny silastic catheter was implanted in 4 dogs in a ramification of an upper jejunal artery providing blood supply to a 5–10 cm jejunal segment 60 cm distally to the ligament of Treitz. In 3 dogs two catheters were implanted for segments 30 and 60 cm below Treitz. The catheter was kept open by a continuous perfusion (1,5 ml/24h) with a diluted heparinic solution (333 IU/ml) by means of an insulin infusion pump which was fixed to the animals protection jacket. After complete recovery of the dogs (at least two weeks after surgery) experiments were performed in conscious fasted animals. Small bowel motility was recorded by means of 10 implanted bipolar electrodes. After a control period with perfusion of saline (1 ml/min) 50, 100 and 200 ng/kg/h Somatostatin was added to the infusion. In the 3 dogs with two catheters 100 and 200 ng/kg/h Somatostatin was tested on each level separately. The Somatostatin perfusion lasted 5h and each dose was tested at least twice. I.v. infusions of Somatostatin followed the same protocol. Intra-arterial infusion of saline did not alter the characteristics of the MMC pattern in the perfused area. In all dogs Somatostatin induced 1-3 ectopic fronts. The induction was dose dependent: 50 ng/kg/h almost never and 200 ng/kg/h almost always induced ectopic activity fronts. The ectopic AF’s always started during the initial period of the perfusion. They originated just distally to the perfusion site and progressed down at a normal propagation velocity 3.1 ±0.3 cm/min vs. 3.4 ±0.3 cm/min (mean + SEM). Later on and in spite of the continued Somatostatin perfusion normal AF’s (starting in the gastroduodenal area) continued to occur.